Is your Gaggia misbehaving? Give us the details here and we will try to help. Include lots of information: how old the machine is, pictures if you have them, what your maintenance regime has been, etc. etc. etc.

This probably should be listed first, since it is more important for making good shots, and may well cost and weigh more than your Gaggia itself.
Do not underestimate the critical aspect of a good burr grinder.